Cheese is a fresh or ripened dairy product consisting predominantly of varying amounts of coagulated milk proteins, fat, water and salts. There is an enormous variety of cheese types of different regional origins, traditions of consumption, chemical composition, texture, taste, flavour and shelf life. Thus, processes for making cheese are different for each different type of cheese to be made.
In principle, there are a number of main steps in the cheese manufacturing process which are essentially the same for all cheeses: Generally, milk intended for the cheese making is pasteurised, i.e. subjected to a heat treatment to kill pathogens and spoilage bacteria such as coliform bacteria which may spoil the cheese by producing large amounts of gas and an unpleasant flavour. The milk is then usually standardised in order to obtain the appropriate ratio of components which is specific for the particular cheese variety.
Subsequently, a microbial starter culture and a milk clotting agent are added to initiate a specific enzymatic proteolysis of milk proteins leading to the destabilisation of the casein micelles and consequently to the coagulation of the milk. Milk clotting agents include native enzymes derived from microbial or animal tissue sources, or the enzymes may be provided as gene products of recombinant cells expressing a milk clotting enzyme of animal or microbial origin.
Starter cultures are often cultures of acid-producing bacteria which are added to the cheese milk in order to provide the pH, desired taste, aroma and texture of the resulting cheese and to reduce the pH of the cheese milk as the activity of the added milk clotting enzyme is higher in acidic media. Furthermore, the reduction in pH brought about by the metabolism of the starter culture organism inhibits the growth of undesirable microorganisms and prevents biochemical reactions.
In addition to the production of acids and flavour compounds, the starter culture organisms also produce and/or contain proteases, peptidases and aminopeptidases that, like a milk clotting agent, degrade the proteins and carbohydrates present in the milk, in a non-specific manner, and which is important for the ripening of the cheese.
After an appropriate time interval, during which the coagulum is cut and stirred, allowing for sufficient syneresis, the whey is drained off. The remaining material is referred to as a curd. Depending on the kind of cheese to be made, the curd is subsequently pressed into a shape and consistency that are characteristic for the particular type of cheese and usually transferred to a brine solution in order to be salted. The pH of a traditional curd is between pH 5.6 and 6.4. Finally, the curd is kept under conditions where the curd undergoes a ripening process to obtain the finished cheese, and the end pH in the cheese will reach 4.9 to 5.3 within the first 48 hours, due to the metabolic activity of the starter culture.
In order to accelerate the ripening of the cheese, which is initiated by the selected starter culture added to the cheese milk, a ripening agent, such as a microorganism or an enzyme may be added to the cheese milk or to the cheese curd. Thus, a ripening agent is only added in addition to a starter culture and/or milk clotting agent.
The choice of starter culture organism is based on tradition, the flavour and texture desired in the cheese and the rate and extent of acid development desired during the entire manufacturing process and in the finished cheese. Useful commercial dairy starter cultures are generally composed of lactic acid-producing lactic acid bacteria. In the present context, the expression “lactic acid bacteria” designates a group of Gram-positive, catalase negative, non-motile, microaerophilic or anaerobic bacteria, which ferment sugar with the production of acids such as lactic acid as the predominantly produced acid, acetic acid, formic acid and propionic acid. The industrially most useful lactic acid bacteria are found among Lactococcus species, Streptococcus species, Enterococcus species, Lactobacillus species, Leuconostoc species and Pediococcus species. The starter culture organisms will continue to ferment sugar until conditions within the cheese prevent it, i.e. unfavourable pH, salt and/or temperature conditions. As the activities of the starter culture organism in general is desired throughout the whole cheese process, i.e. both during the coagulation of the milk proteins and during cheese ripening, the conditions within and around the cheese are carefully selected in order to prevent the killing of all the added organism.
It is evident from the above description of the traditional cheese making process that the different activities of the added starter culture organism to the cheese milk initiate the cheese ripening processes and thus to a large extent determine the pH, taste, flavour, aroma and texture characteristic of the resulting cheese curd and cheese type. This means that the type of cheese is determined at an early stage of the process namely when the starter culture is added to the cheese milk.
The dairy plant must therefore decide at an early stage of the cheese making process, i.e. prior to adding the starter culture to the cheese milk, which type of cheese it is desired to make. This implies that the dairy plant is restricted to produce only one type of cheese at a time and/or one type of cheese for each processing line. However, in the dairy industry there is a clear trend towards larger production units, which are designed to produce cheese at the shortest possible time, which are more cost effective and flexible and which can be operated with little manpower.
It is therefore an important objective of the present invention to provide an improved method of providing a cheese, which is adapted to the increasing demand for higher flexibility in the modern cheese production. The present method gives the dairy plant the possibility at a later stage, i.e. after the cheese curd has been obtained and/or at the ripening stage of the cheese curd, of the cheese manufacturing process to decide which cheese type to produce. Furthermore, the present method implies that the dairy plant can produce a range of different types of cheese based on a single batch of cheese curd. In addition, more curd per working hour can be produced using the same equipment, automation of the process can be introduced more readily and be used more safe/homogeneous with less hazards and bacteriophage attacks, which are a common problem in traditional cheese production methods, can be eliminated. Furthermore, the method provided herein implies that the dairy plant operators can more easily control the ripening of the cheese.
The method according to the present invention is based on the surprising findings that the cheese type can be determined at a later stage of the cheese manufacturing process by initially preparing a cheese curd using a curdling agent and subsequently, after the curd has been obtained, introducing into the cheese curd a lactic acid bacterial starter culture in order to bring about the main ripening of the cheese, the activity of which culture is thereby determining the desired pH, texture and sensory parameter such as taste, flavour and aroma of the resulting cheese. As the lactic acid bacterial starter culture is introduced into the cheese curd, the taste and texture characteristic of the resulting cheese are determined at a late stage of the cheese making process. This implies that it is possible to produce one large batch of cheese curd which may subsequently be divided into smaller portions each of which can be inoculated with different conventional or specifically designed lactic acid bacterial starter culture to obtain different types of cheese or different ripening profile (storage time) based on the same cheese starting material.
Various processes for preparing a cheese are known in the art wherein a cheese ripening agent, e.g. a mould or an enzyme such as a lipase, is added to a conventionally produced curd prior to ripening. DE 195 46 345 describes a method for the manufacturing of Blue cheese. According to the traditional Blue cheese manufacturing, e.g. the Danablue process, a starter culture organism, a milk clotting agent and spores of P. roqueforti are added to the cheese milk subsequent to the coagulation and salting steps the resulting cheese curd is exposed to air due to piercing of the cheese. In DE 195 46 345 the fungal spores are added in combination with the piercing. Besides focusing on giving the best opportunities for the P. roqueforti spores to survive in the Blue cheese, this process involves the use of a traditional cheese curd prepared by using a traditional starter culture and a milk clotting agent added to the cheese milk.
Another example of a cheese manufacturing process is described in U.S. Pat. No. 3,973,042 wherein a mixture of a microbial lipase and spores of P. roqueforti is added to a traditionally produced cheese curd after draining off the whey. In this disclosure the lipase is important for obtaining the characteristic rancid taste in the Blue cheese.
Accordingly, the cheese industry has until now not been in the possession of a process for the manufacturing of cheese wherein a lactic acid bacterial starter culture is added to the cheese curd. Thus, it has until now not been possible to determined the cheese type at a late or different stage of the process by adding a lactic acid bacterial starter culture to the cheese curd. Reason for this may be traditional way of thinking and conservatism in the cheese industry as it is not common to change the old traditional cheese-manufacturing processes.